Like "I have 4 different brands of meters. Most have an error margin of +/- 20%. As an example, if your bg was actually 100, and you did several tests with any of these meters, Your readings could be anywhere from 80 to 120. The meter would be operating within specs. +/- 20% is what most manufacturers design into their meters. This is stated in the manual that comes with most meters including the one touch. Also, most meters are plasma-calibrated which will make it a bit easier to compare to most lab tests. Some meters are whole blood calibrated and that will alter the comparison to some extent."